A well-known patterning method employs a droplet ejecting device for forming a wiring pattern on a substrate. The droplet ejecting device generally drops onto a substrate liquid containing a functional material such as silver particles, thereby fixing the functional material on the substrate to form a wiring pattern. Such a patterning method is described, for example, in Japanese Patent Application Laid-Open Publication No. 2002-164635. The method enables cost effective wiring patterning requiring only a simple mechanical configuration as compared to a vapor deposition method using a shadow mask.
FIGS. 12A to 12C are cross-sectional views of a major part of a conventional droplet ejecting device. The respective views illustrate a process of droplet formation and ejection from a pressure chamber 910 through a nozzle 930. In the figures, a droplet ejected from nozzle 930 is assumed to have a volume of 10 pl (picolitter: 10−15 m3). As shown in FIG. 12A, a surface 912 of pressure chamber 910, and which is in connective communication with a liquid tank 900, is deformed by means of a piezoelectric element 920 in a direction away from the interior of the chamber 910 to become convex, whereby a liquid in pressure chamber 910 is depressurized, and the liquid is allowed to flow from liquid tank 900 into pressure chamber 910. Conversely, in FIG. 12B, surface 912 of pressure chamber 910 is deformed by means of piezoelectric element 920 in a direction towards the interior of the chamber 910 to become concave, whereby the liquid in the chamber 910 is subject to increased pressure. As a result, a column of the liquid is caused to protrude from nozzle 930. As shown in FIG. 12C, when the liquid in pressure chamber 910 is again depressurized, the liquid column retracts into pressure chamber 910 through nozzle 930. During retraction, the liquid column separates at a neck portion formed under an inertial force, and a droplet is ejected from an ejecting head.
A liquid generally used for the patterning of the wiring contains a large quantity of fine conductive particles such as silver particles. That is, the liquid used for patterning is generally of a relatively high viscosity as compared to, for example, pigment type ink; and may have a viscosity of as high as 20 mPa·s (Pascal per second). To achieve high-precision wiring patterning, it is necessary to eject microscopic droplets from a droplet ejecting device.
However, the higher the viscosity of a liquid from which droplets are ejected from a droplet ejecting device, the more difficult it is to form a droplet of a sufficiently small volume (i.e., to micronize a droplet), which makes it difficult to carry out high-precision patterning. An example of this problem is illustrated in FIGS. 13A and 13B. The figures show a failure to create a microscopic droplet of about 2 pl from a high viscosity liquid being ejected from a droplet ejecting device. As described above, when a liquid in pressure chamber 910 is depressurized and then pressurized, a liquid column protrudes from nozzle 930 (see FIG. 13A). However, since an intermolecular force acting within a high viscosity liquid is large, the liquid column retracts into pressure chamber 910 without droplet separation taking place, even if the liquid in pressure chamber 910 is once again depressurized (see FIG. 13B).
In an attempt to overcome this problem it is possible to increase a speed at which a liquid column is ejected, or alternatively it is possible to increase a volume of the column. However, neither approach provides a satisfactory result. If the ejection speed of the liquid column is increased, spattering tends to result; also the ejected liquid droplets tend to shift from their intended trajectory and hit the substrate inaccurately. In the case of increasing a volume of the liquid column, it becomes impossible to form microscopic droplets. Thus, to date, a droplet ejecting device that is capable of micronizing droplets from a high viscosity liquid has not been available.